If you bought the game from STEAM try this:Exit from STEAM, turn STEAM off.Reopen STEAM, wait for loading process. Now go to library, or store page press play, i think (or it start automaticaslly). Now you can download the game. No need cdkey, because the key is kinda tieded to your email.When the download it's finished just press play. You will see a pop up screen, insert email and password and start to play.